This invention relates to an improved toll restrictor. More particularly, it relates to a toll restrictor having infinite input impedance during on-hook conditions and utilizes circuitry features which prevent the making of long distance calls normally allowed because of central office timeout and further prevent improper restricting as well as providing standard toll restricting functions.
Toll restrictors and call divertors are provided to overcome the problem of the use of telephones for unauthorized long distance calls. These long distance calls, of course, result in tolls charged to that telephone number.
Some of the first toll restrictors merely utilized a switch in series with either the tip or ring conductor of a telephone. The switch could be placed in a lockbox with only authorized personnel having the key to the box. Of course, this would not permit even local calls when the switch was open. More sophisticated electronic toll restrictors have also been provided. One example of such a restrictor is shown in U.S. Pat. No. 3,757,055. This patent shows a means of restricting an outgoing call if the digit zero is dialed on any of the first three dial pulls, as well as a means for restricting the call if more than eight digits are dialed. However, various techniques have been devised to defeat this type as well as other prior art electronic toll restrictors. For example, the subscriber may dial a digit and wait until the central office times out the call which, in effect, restores the dial tone. The prior art toll restrictor would have sensed this digit and treated it as the digit of the first pull. By using this slow dialing technique, a zero may be dialed, say on the fourth pull, which is normally not restricted. The toll restrictor would see it as the fourth pull, however, the central office would see it as a first dial pull and give access to the operator, thus defeating the toll restrictor.
Also, there have been problems in digit counters giving false indications of a digit to be restricted. For example, if the digit three is to be restricted and the number four is dialed, some counters will provide an output pulse as the counter passes the three count en route to four, thus causing a false indication of restriction.
Prior art toll restrictors and other devices which sense telephone signals are normally attached in parallel to the telephone line, i.e., across the tip and ring conductors. These devices have a finite input impedance. It has been alleged that these can cause problems in the transmission characteristic in the communication lines, such as wave reflections and other distortions.
It is, therefore, desirable to provide a toll restrictor which overcomes these and other problems of prior art.
In the use of the term "restrictor", normally one thinks of disconnecting the telephone handset from the central office by a switch when a call is to be restricted. However, the device set forth herein may also be used to divert outgoing calls from the handset to some prerecorded message, so as to indicate to the caller that he is trying to make a restricted call, or to some other diversion. Furthermore, the restrictor may shunt or open the line or provide other mechanisms for prohibiting the transmission of an unauthorized long distance call. Therefore, the term restrictor should be interpreted in its broadest sense, which would at least include all of the above.